A light modulation device, in which a light modulation layer including a liquid crystal compound or the like is positioned between two substrates facing each other, has been used for various applications.
For example, in Patent Document 1 (EP Patent Application Publication No. 0022311) a variable transmittance device using a so-called GH cell (guest host cell), in which a mixture of a liquid crystal host material and a dichroic dye guest is applied, as a light modulation layer has been known.
In such a device, a glass substrate having excellent optical isotropy and good dimensional stability has mainly been used as the substrate.
There is an attempt to apply a polymer film substrate instead of a glass substrate as a substrate of the light modulation device, while the application of the light modulation device is extended to eyewear or a smart window such as a sunroof without being limited to the display device and the shape of the device is not limited to a plane, but various designs such as a folding form are applied thereto, with showing the necessity of a so-called flexible device or the like.
In the case of applying the polymer film substrate, it is known that it is advantageous to apply a film substrate which is as optically isotropic as possible and has a small difference in physical properties in so-called MD (machine direction) and TD (transverse direction) directions in order to secure characteristics similar to those of a glass substrate.